One-way delay measurement system for local area network delay and jitter characterization

Abstract

The IEEE 1588 Standard for A Precision Clock Synchronization Protocol for Networked Measurement and Control Systems (PTP) has been developed to provide better quality in-band clock synchronization in distributed measurement and control systems and other network embedded systems. Using IEEE 1588 compliant Ethernet equipment (network interface cards and switches) it is possible to provide sub 1 microsecond precision of slave clocks compared to a reference clock. The centerpiece of an IEEE 1588 based clock is the clock servo disciplining the local clock based on the information provided by IEEE 1588 about the reference time. However, it is an opened question how precision can be increased even further by advanced clock servo design. Furthermore, as only a minority of office and industrial Ethernet switches support IEEE 1588, it is also paramount to investigate the achievable performance for such systems, which is also defined by the clock servo.To design advanced control systems the plant and the disturbances must be modeled, and the model must be built based on representative measurements. In our case, the one-way network delay in between the reference clock and the slave clock must be characterized in Local Area Networks (LAN) for typical network load scenarios for advanced servo design, so 1-10 ns accurate one-way delay and jitter measurements must be achieved for this application. Measuring one-way delay in Local Area Networks requires specialized and expensive equipment; however, we will show that it is possible to build such measurement system using commercial off-the-shelf (COTS) components and open source software. Our system uses Intel network interface cards, the open source Linux operating system, and some self-developed software components (both Linux kernel drivers and user space programs).